1. Field of the Invention
This invention relates to gel systems and especially to edible gel systems that can be used, for example, in food products for human or animal consumption.
2. Prior Art
The microbial polysaccharide obtained from Pseudomonas elodea is commercially produced by the Kelco Corporation and marketed under the trade name Gellan.
Gellan is commercially available both in its native (fully acetylated) form and in wholly or partially deacetylated form. For the purposes of this application the expression "high acetyl gellan" is used for the fully acetylated native form and "low acetyl gellan" is used for the wholly or partially deacetylated forms.
The production of the polysaccharide in native and deacetylated form and its structure are described in U.S. Pat. Nos. 4,326,052 and 4,326,053 (Kang), the disclosure whereof is hereby incorporated by reference.
Weak but elastic aqueous gels can be produced from high acetyl gellan. Firm but brittle aqueous gels comparable to those that can be obtained from agar or carrageenan can be produced from low acetyl gellan, the lower the acetyl content the greater the strength and brittleness of the gel. Deacetylation to only slight extents, for example, 15% has significant effects on the strength and brittleness of the gel. For many applications, however, a brittle gel is undesirable and a strong elastic gel with a texture comparable to that produced from gelatin is required.
It is well known that while certain polysaccharide gums can be used to form gels others will not form gels on their own. However, certain combinations of polysaccharide gums have been found to form gels even though one or more of the gums will not form a gel on its own. A synergistic effect has been found with certain polysaccharide gums whereby adding a non-gelling gum to a gelling gum a significant increase in gel strength is obtained. Gels can also be produced from certain combinations of gums of which none of the individual gums will form gels. In this manner combinations of polysaccharide gums or polysaccharide gums with other gelling agents can produce gels with desirable textures and/or strength. Carob gum, will not gel on its own but in combination with agar or carrageenan will produce a much stronger and more elastic gel than is obtained from agar or carrageenan alone. Moreover, xanthan gum will not form a gel on its own but in combination with certain galactomannan gums such as carob, tara and cassia gums, which will also not form gels on their own, produces useful gels.
Glucomannan gums will produce thermo-irreversible gels under strongly alkaline conditions. In combination with xanthan gum, however, strong thermo-reversible gels can be produced under acid to neutral conditions.
It has been observed in the literature that combinations of gellan with small amounts of other gums such as xanthan guar or carob gum will reduce syneresis in a gel but no marked improvement in the strength or texture of the gel is observed. U.S. Pat. No. 4,517,216 (Shim), the disclosure whereof is hereby incorporated by reference, discloses that the only gelling agent that produces any synergistic improvement in gel strength when used in combination with gellan is gelatin. This patent specification discloses that many gelling agents were tested by the applicants, in combination with gellan to try to achieve a synergistic increase in gel strength, including carrageenan, carob gum, sodium alginate, corn starch and pectin. Of these only carrageenan gave a small increase in gel strength, but this was considered to be primarily because of the presence of various salts in the carrageenan affecting gelling of the gellan rather than the carrageenan itself. All of the other agents tested reduced gel strength. Moreover, the effect with gelatin was only noticed with low acetyl gellan.